Bump xunit from 2.5.2 to 2.6.0

Bumps [xunit](https://github.com/xunit/xunit) from 2.5.2 to 2.6.0.
- [Commits](xunit/xunit@2.5.2...2.6.0)

---
updated-dependencies:
- dependency-name: xunit
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

tests/Serilog.Formatting.Log4Net.Tests.csproj

@@ -17,7 +17,7 @@
     <PackageReference Include="Serilog.Enrichers.Environment" Version="2.3.0" />
     <PackageReference Include="Serilog.Enrichers.Thread" Version="3.1.0" />
     <PackageReference Include="Verify.Xunit" Version="22.1.4" />
-    <PackageReference Include="xunit" Version="2.5.2" />
+    <PackageReference Include="xunit" Version="2.6.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" PrivateAssets="all" />
   </ItemGroup>